The invention relates to the measurement of capillary related interstitial fluid using ultrasound methods, compositions and devices, particularly methods, compositions and devices that provide for the measurement and monitoring of edema in tissues, especially a capillary related edema layer in a human.
Edema underlies a myriad of human medical conditions. Yet, despite the relatively common occurrence of edema, and its potentially life threatening nature, accurate and reliable assessments of edema are not available to the clinician or patient alike. Traditionally, methods have consisted of visual inspection of the extremities, tissue palpation by a clinician, and measurement of the circumference of the extremity. Although these methods are familiar assessments to clinicians, none of these methods is quantitative and all suffer from tremendous variability due to inter- and intra-clinician variability of the measurements.
Visual inspection of the affected body region yields information on changes in the color and texture of the skin. Skin changes in patients with edema include discoloration and ulceration. Unfortunately, such skin changes occur typically only in patients with long-standing, chronic edema and are not useful for diagnosing early or discrete edema. Furthermore, skin changes are difficult to assess on a quantitative scale and are not useful for monitoring a response to treatment of edema or the underlying cause of the edema.
Visual inspection can also yield information on arteries and veins, e.g. varicose veins may be visible and may be identified as a potential cause for capillary related edema. Such identification of vascular pathology, unfortunately, is only qualitative, is limited to assessment of the vascular system, and cannot provide information on the patient""s fluid status or on cardiac, renal or hepatic performance.
Manual palpation can be used to evaluate edema. For manual palpation, a finger is pressed gently but firmly into the patient""s skin and subjacent tissue. The depth of the resultant indentation and persistence of the indentation after the finger has been released yield information on the severity of the edema. A semiquantitative scale can be used to assess the severity of the edema, typically consisting of five different grades: I.) absent, II.) slight, III.) mild, IV.) moderate, and V.) severe (see Bates et al., J. B. Lippincott, 1995). Results obtained with manual palpation are, however, subjective and difficult to reproduce.
Circumference measurements of appendage regions and limbs have also been employed for assessing edema. These measurements of changes in circumference of a limb or an appendage region are limited to detecting large increases in interstitial fluid. Subtle increases or also decreases in interstitial fluid in early or mild forms of capillary related edema will be masked since the change in circumference induced by the interstitial fluid shift (usually on the order of few millimeters or less) will be small compared to the overall circumference of the appendage region or limb (usually on the order of several centimeters or decimeters).
Consequently, the present inventors have recognized the need, among other things, to provide reliable, quantitative and accurate ultrasound devices and methods for such applications, particularly hand held devices capable of being operated by untrained operators. The methods and devices provided herein permit continuous, cost effective monitoring and accurate measurement of capillary related interstitial fluid of patients in a variety of diverse clinical settings.
CROSS REFERENCE TO RELATED APPLICATIONS
TECHNICAL FIELD
BACKGROUND
SUMMARY
BRIEF DESCRIPTION OF FIGURES
DETAILED DESCRIPTION OF THE INVENTION
1.0 ABBREVIATIONS AND DEFINITIONS
2.0 INTRODUCTION
3.0 METHODS AND DEVICES FOR MEASURING CAPILLARY RELATED INTERSTITIAL FLUID
Application Sites
Application to Medical Treatments
Different Types of Monitoring
Calculations and Standards
Empirical Methods for Determining Standards
4.0 METHODS AND DEVICES FOR MEASURING CAPILLARY RELATED EDEMA
Anatomical Regions
Use in Medical Conditions and Treatments
Devices for Testing for Capillary Related Edema
Calculations and Standards
5.0 METHODS AND DEVICES FOR MEASURING VASCULAR PERFORMANCE
6.0 METHODS AND DEVICES FOR EVALUATING CARDIAC PERFORMANCE
7.0 METHODS AND DEVICES FOR MEASURING RENAL DISORDERS AND FUNCTION
8.0 METHODS AND DEVICES FOR MEASURING HEPATIC DISORDERS AND FUNCTION
9.0 METHODS AND DEVICES FOR MULTISITE MONITORING
10.0 ULTRASOUND PROBES FOR IN SITU MEASUREMENTS
EXAMPLES
GENERAL MATERIALS AND METHODS
EXAMPLE 1: ULTRASONOGRAPHIC MEASUREMENT OF TISSUE THICKNESS IN AN IN VITRO MODEL OF CAPILLARY RELATED EDEMA
EXAMPLE 2: ULTRASONOGRAPHIC MEASUREMENT OF THICKNESS OF CAPILLARY RELATED EDEMA IN A MODEL OF VENOUS INSUFFICIENCY AND RIGHT VENTRICULAR CARDIAC FAILURE
EXAMPLE 3: ULTRASONOGRAPHIC MEASUREMENT OF THICKNESS OF PRETIBIAL EDEMA IN A MODEL OF CAPILLARY RELATED EDEMA SECONDARY TO ABNORMAL COLLOID OSMOTIC PRESSURE AND/OR RENAL FAILURE
PUBLICATIONS
U.S. PATENT DOCUMENTS
FOREIGN PATENT DOCUMENTS
OTHER PUBLICATIONS
CLAIMS
ABSTRACT
The present invention recognizes for the first time that ultrasound can be applied to the measurement of capillary related interstitial fluid. The invention finds particular application for convenient and cost effective measurements in a variety of clinical settings. Previously, it was not recognized that diagnostic ultrasound measurements of capillary related interstitial fluid were possible, or precise. Nor was it recognized that clinically rapid shifts in capillary related interstitial fluid distribution in tissues could be monitored using ultrasound methods or devices. The invention includes monitoring of capillary related interstitial fluid in a subject using ultrasound wave devices and methods as described herein. Aspects of the invention are directed to continuous or intermittent monitoring, such as capillary related edema monitoring in a human.
In one embodiment, the invention includes a method of measuring capillary related interstitial fluid comprising: transmitting at least one ultrasound signal to a tissue in a subject in need of capillary related interstitial fluid assessment, recording at least one ultrasound signal from the tissue, and determining a capillary related interstitial layer thickness from a first reflective surface to a second, usually an internal, reflective surface, wherein the capillary related interstitial layer thickness is an assessment of capillary related interstitial fluid. Typically, such a subject will be a human desiring a capillary related interstitial fluid assessment because a clinician wishes to use the invention as a part of a diagnosis or the subject wishes to perform a self assessment of the subject""s capillary related interstitial fluid.
The inventors were also the first to recognize that ultrasound methods and devices could be applied to the assessment of different aspects of integrated cardiac, vascular, renal or hepatic function. Numerous aspects of the present invention circumvent many of the disadvantages of the current techniques for evaluating dynamic performance of the heart or vascular system.
For example, the present invention provides for a noninvasive assessment of vascular performance that is relatively inexpensive, easily performed by a clinician (not necessarily a physician trained in ultrasound techniques) and can integrate tissue effects into the assessment, especially capillary related tissue effects. Typically, a test of vascular performance, includes two basic steps: reducing or increasing blood flow (or pressure) to a tissue in a subject in need of vascular performance assessment (step (a)), and monitoring an interstitial layer thickness (ILT) of the tissue (step (b)). Monitoring ILT with an ultrasound probe can be before, after or concurrent with reducing or increasing blood flow in step (a).
Other techniques and devices are described herein for assessments of cardiac, renal, capillary and hepatic function. Such aspects of the invention can also be used to assess the effect of medical treatments on such physiological functions.
The invention also provides for the first time methods and devices for multisite monitoring of different anatomical regions either concurrently or at predetermined time intervals. Monitoring anatomical changes during clinically relevant time periods or continuous monitoring provide an important diagnostic tool for detecting short or rapid changes in tissue structure, particularly interstitial layer thickness. In contrast to previous work, the invention is able to measure rapid changes in ILT and monitor ILT from different anatomical regions simultaneously or within short time frames to compare ILTs from different regions.
In one aspect, the invention provides for a method of multisite monitoring of ILT. The method comprises transmitting an ultrasound pulse from a first ultrasound probe to a first anatomical region and transmitting an ultrasound pulse from a second ultrasound probe to a second anatomical region. The method includes recording ultrasound signals from a first ultrasound probe to a first anatomical region and recording ultrasound signals from a second ultrasound probe to a second anatomical region. The method also includes monitoring interstitial layer thickness from the first and second, or more, anatomical regions. Typically, the method is practiced by monitoring from the first anatomical region concurrently with monitoring from the second anatomical region.
Another related aspect of the invention includes a multi-probe set that may be used for multi-site monitoring. The multi-probe set comprises a first ultrasound probe comprising a first output port, the first ultrasound probe adapted for continuous or in situ monitoring at a first anatomical region and a second ultrasound probe comprising a second output port, the second ultrasound probe adapted for continuous or in situ monitoring at a second anatomical region. The set can include an ultrasound system to concurrently process first signals from the first ultrasound probe and second signals from the second ultrasound probe. Systems or sets with more than two probes can also be used. Each probe in the set can be adapted for a particular anatomical region or indication. For example, the anatomical region can be selected from the group consisting of the forehead region, anterior tibia region, foot region, distal radius region, elbow region, presternal region and temporal bone region. Preferably, the ultrasound probe is a micro-transducer adapted for monitoring interstitial layer thickness.
The invention provides for the first time micro-transducers applied to the skin of a subject for ultrasound measurements of tissue structure. Typically, the micro-transducers are adapted for either monitoring ILT or capillary related edema, usually on the skin in a predetermined anatomical region. As described herein, the micro-transducers are typically small about 10 to 20 mm2 or less in surface area, not hand-held but rather attachable to the skin surface, and light weight. Preferably, micro-transducers are isolated and not connected to an ultrasound system or display by a conductive wire, as described herein. In use, the micro-transducers are usually secured to the skin of a subject for continuous monitoring of the interrogated region.